1. Field of the Invention
The present invention relates to a navigation apparatus and method, such as an on-vehicle type navigation apparatus, and further relates to a computer program product for the navigation apparatus and/or method. More specifically, the present invention relates to a navigation apparatus and method improved in handling of map data used for a navigation processing, and further relates to a computer program product for performing the navigation processing.
2. Description of the Related Art
Navigation apparatuses, particularly on-vehicle type navigation apparatuses, are now becoming increasingly common under rapid-paced development. A navigation apparatus displays a current position of a navigation object, for example a current position of a car on which the navigation apparatus is mounted, on a display device, such as a display screen, and provides various functions including route guidance and the like, by means of map data stored in a CD-ROM or DVD-ROM. With regard to a way of obtaining the current position of the object, typically used is either one or both of (i) a stand-alone type (i.e., a built-in, self-sustained or dead-recognizing type) navigation system in which the current position of the object is measured only using information from sensors that are mounted on the navigation object to detect various parameters such as velocity, azimuth and the like and (ii) a navigation system with a navigation aid system using a GPS (Global Positioning System) in which the current position is obtained by receiving measurement data transmitted from a plurality of satellites.
On the other hand, a KIWI-format is proposed as a common format of map data used for the navigation apparatus, particularly the on-vehicle type navigation apparatus. This KIWI-format is proposed by navigation makers at home and abroad so as to provide map data independently of application software. That is, the format is constructed so as to be applied to various kinds of navigation apparatus, regarding versatility and extensibility. The KIWI-format or other format having the same idea as the KIWI-format is in widespread use among the map data used for the navigation apparatus.
On the other hand, there is proposed a technique to use map data in which the latest road data is reflected by updating the map data with difference data (e.g., as disclosed in Japanese Patent Application Laid-Open No. 2001-229369). Herein the “difference data” in the map data means a part of data (map data portion) different between a state of map data before updating and another state of map data after updating. In this technique, a state of map data that is generated at a predetermined time point is assumed to be original data, while difference data representing a change in real road conditions from the time point at which the original data is generated is independently generated. In the case that the map data is actually used, the change in the road conditions represented by the difference data is reflected into the original data. It is considered that the map data reflecting the latest road conditions can be obtained and utilized relatively efficiently by using the difference data.
Nevertheless, the difference data at present has such a data structure that it enforces, on the navigation apparatus, searching the entire difference data for appropriate difference data with respect to of the original data, and thereby using only the searched difference data. Thereby, a heavy task is imposed on the navigation apparatus to reflect the difference data, causing a technical problem of reduction in a processing speed of the navigation apparatus as a whole, or another problem of requiring an expensive processing device for a higher-speed processing.
Additionally, merging a form of data with the original data to reflect the difference data as mentioned above may cause a deviation in size, format or arrangement of data in the KIWI-format or the like. Therefore, technical problems arise, including a problem that the navigation apparatus reduces its processing speed, and a problem that the navigation apparatus fails completely or partly to recognize, as normal map data, the map data with a deviation or disorder due to the reflection of the difference data.